Requirements for the use of alternative energy or clean energy have increased due to the rapid increase in the use of fossil fuels, and, as a part of this trend, power generation and electricity storage using an electrochemical reaction are the most actively researched areas.
Currently, a typical example of an electrochemical device using the electrochemical energy may be a secondary battery and there is a trend that its usage area is expanding more and more. In recent years, demand for secondary batteries as an energy source has been significantly increased as technology development and demand with respect to portable devices, such as portable computers, mobile phones, and cameras, have increased. Among these secondary batteries, lithium secondary batteries having high energy density, high operating potential, long cycle life, and low self-discharging rate have been subjected to considerable research and have been commercialized and widely used.
Also, in line with growing concerns about environmental issues, a significant amount of research into electric vehicles and hybrid electric vehicles, which may replace vehicles using fossil fuels, such as gasoline vehicle and diesel vehicle, one of major causes of air pollution, has been conducted. Nickel-metal hydride secondary batteries have been mainly used as power sources of the electric vehicles and hybrid electric vehicles. Especially, research into the use of lithium secondary batteries having high energy density and discharge voltage has been actively conducted and some of the research are in a commercialization stage.
A typical lithium secondary battery uses graphite as a negative electrode active material, and charge and discharge of the lithium secondary battery is performed while a process of intercalating and deintercalating lithium ions from a positive electrode into and out of a negative electrode is repeated. Although there is a difference in theoretical capacity of the battery according to the type of electrode active materials, charge and discharge capacities may be generally reduced as cycles proceed.
As the related art, a negative electrode active material for a lithium secondary battery, which includes spheronized natural graphite particles in which flaky natural graphite fragments are structured in the shape of a cabbage on a surface portion thereof and a random shape in the center thereof and granulated; and spheronized natural graphite-modified composite particles including amorphous or semicrystalline carbon, wherein a gap between the flaky natural graphite fragments by sonication is present in the surface portion of the spheronized natural graphite particles, surfaces of the spheronized natural graphite particles are coated with the amorphous or semicrystalline carbon, and the amorphous or semicrystalline carbon is present in the gap so as to maintain the gap existing in the surface portion of the spheronized natural graphite particles, and a method of preparing the same have been proposed.
However, since the amorphous carbon appears outside the negative electrode active material, the efficiency of the secondary battery may be reduced and electrolyte solution consumption may be increased.
Thus, there is a need to develop a negative electrode active material which has a high initial efficiency and low diffusion resistance of lithium ions while reducing the electrolyte solution consumption.